Drive unit

ABSTRACT

A drive unit is disclosed. The drive unit includes a prime mover, a torque converter, and a power transmission mechanism. A torque is inputted from the prime mover to the torque converter. The power transmission mechanism is disposed between the prime mover and the torque converter. The power transmission mechanism is configured to transmit the torque outputted from the torque converter toward a drive wheel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2019-074898, filed on Apr. 10, 2019. The contents of that applicationare incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a drive unit.

BACKGROUND ART

In well-known electric cars, a torque, outputted from a motor, istransmitted to drive wheels through a reducer and a differential gear.For example, in an electric car disclosed in Japan Laid-open PatentApplication Publication No. 2013-60996, the reducer is directlyconnected to the motor, and a torque is transmitted from the reducer tothe drive wheels through the differential gear.

It has been demanded to enhance a driving force in such an electric caras described above. In view of this, it is an object of the presentinvention to provide a drive unit capable of enhancing a driving force.

BRIEF SUMMARY

A drive unit according to an aspect of the present invention includes aprime mover, a torque converter and a power transmission mechanism. Thetorque converter is a component to which a torque is inputted from theprime mover. The power transmission mechanism is disposed between theprime mover and the torque converter. Besides, the power transmissionmechanism transmits the torque outputted from the torque convertertherethrough toward a drive wheel.

According to this configuration, a torque is outputted from the primemover toward the drive wheel through the torque converter. Hence, adriving force can be enhanced. Besides, the torque converter amplifiesthe torque inputted thereto from the prime mover and outputs theamplified torque to the power transmission mechanism. Hence, the torqueconverter is normally disposed between the prime mover and the powertransmission mechanism. By contrast, in the present invention, the powertransmission mechanism is disposed between the prime mover and thetorque converter. In other words, attaching the torque converter isenabled without greatly changing the layout of the prime mover and thepower transmission mechanism in well-known electric cars. It should benoted that in general, the prime mover is disposed on one side of thepower transmission mechanism, whereas an unused space exists on theother side of the power transmission mechanism. Because of this, theunused space can be effectively utilized for disposing the torqueconverter in the present invention.

Preferably, the power transmission mechanism is a reducer.

Preferably, the drive unit further includes an output shaft and an inputshaft. The output shaft outputs the torque outputted from the torqueconverter. The input shaft extends from the prime mover and inputs thetorque from the prime mover therethrough to the torque converter.

Preferably, the output shaft extends from the torque converter towardthe prime mover.

Preferably, the output shaft has a cylindrical shape. Besides, the inputshaft extends in an interior of the output shaft.

Preferably, the torque converter includes a cover, an impeller and aturbine. The cover is a component to which the input shaft is fixed. Theimpeller is unitarily rotated with the cover. The turbine is opposed tothe impeller.

Preferably, the impeller is disposed closer to the prime mover than thecover.

Preferably, the power transmission mechanism includes a planetary gearmechanism and a clutch. The planetary gear mechanism includes a sungear, a planet gear, a planet carrier and a ring gear. The clutch isconfigured to brake rotation of the ring gear. The sun gear is unitarilyrotated with the input shaft. The planet carrier is unitarily rotatedwith the output shaft.

Preferably, the clutch is a one-way clutch. The clutch is configured tomake the ring gear rotatable in forward rotation of the input shaft andthe output shaft. Besides, the clutch is configured to make the ringgear non-rotatable in reverse rotation of the input shaft and the outputshaft.

Overall, according to the present invention, a driving force can beenhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a drive unit.

FIG. 2 is a cross-sectional view of the drive unit.

FIG. 3 is a cross-sectional view of a torque converter.

FIG. 4 is a cross-sectional view of a type of impeller hub.

FIG. 5 is a cross-sectional view of another type of impeller hub.

FIG. 6 is a cross-sectional view of the drive unit shown for indicatinga first cooling flow pathway.

FIG. 7 is a cross-sectional view of a sidewall portion of a type ofcover.

FIG. 8 is a cross-sectional view of a sidewall portion of another typeof cover.

FIG. 9 is a schematic diagram of a drive unit according to amodification.

FIG. 10 is a schematic diagram of a first one-way clutch according toanother modification.

FIG. 11 is a schematic diagram of a drive unit according to yet anothermodification.

DETAILED DESCRIPTION

A preferred embodiment of a drive unit according to the presentinvention will be hereinafter explained with reference to drawings. FIG.1 is a schematic diagram of the drive unit according to the presentpreferred embodiment, whereas FIG. 2 is a cross-sectional view of thedrive unit according to the present preferred embodiment. It should benoted that in the following explanation, the term “axial direction”refers to an extending direction of a rotational axis O of a prime mover2 and a torque converter 3. On the other hand, the term “circumferentialdirection” refers to a circumferential direction of an imaginary circleabout the rotational axis O, whereas the term “radial direction” refersto a radial direction of the imaginary circle about the rotational axisO. Moreover, the term “forward rotation” refers to rotation in forwardmovement of a vehicle, whereas the term “reverse rotation” refers torotation in backward movement of the vehicle.

[Drive Unit 100]

As shown in FIGS. 1 and 2, a drive unit 100 includes the prime mover 2,the torque converter 3, a reducer 4 (exemplary power transmissionmechanism), an input shaft 5, an output shaft 6, a torque convertercasing 7, a hydraulic fluid sump 8 and a first cooling flow pathway 9 a.The drive unit 100 is installed in, for instance, an electric car. Thedrive unit 100 transmits a torque, outputted from the prime mover 2, todrive wheels 101. It should be noted that the torque converter 3, thetorque converter casing 7, the hydraulic fluid sump 8 and the firstcooling flow pathway 9 a will be collectively referred to as a torqueconverter unit.

<Prime Mover 2>

The prime mover 2 includes a prime mover casing 21, a stator 22 and arotor 23. In the present preferred embodiment, the prime mover 2 is amotor. Detailedly, the prime mover 2 is a so-called inner rotor motor.The prime mover casing 21 is fixed to a vehicle body frame or so forthand is non-rotatable.

The stator 22 is fixed to the inner peripheral surface of the primemover casing 21. The stator 22 is non-rotatable. The rotor 23 is rotatedabout the rotational axis O. The rotor 23 is disposed radially insidethe stator 22.

<Torque Converter 3>

The torque converter 3 is disposed at an interval from the prime mover 2in the axial direction. The reducer 4 is disposed between the torqueconverter 3 and the prime mover 2. The rotational axis O of the torqueconverter 3 is substantially matched with that of the prime mover 2. Thetorque converter 3 is a device to which the torque, outputted from theprime mover 2, is inputted. Additionally, the torque converter 3amplifies the torque inputted thereto from the prime mover 2, andoutputs the amplified torque to the reducer 4.

As shown in FIG. 3, the torque converter 3 includes a cover 31, animpeller 32, a turbine 33, a stator 34, a first one-way clutch 35 and asecond one-way clutch 36. Besides, the torque converter 3 furtherincludes a centrifugal clutch 37.

The torque converter 3 is disposed such that the impeller 32 faces theprime mover 2 (the left side in FIG. 3) whereas the cover 31 facesopposite to the prime mover 2 (the right side in FIG. 3). The torqueconverter 3 is accommodated in the interior of the torque convertercasing 7. Hydraulic fluid is supplied to the interior of the torqueconverter 3. The hydraulic fluid is, for instance, hydraulic oil.

The cover 31 is a component to which the torque, outputted from theprime mover 2, is inputted. The cover 31 is rotated by the torqueinputted thereto from the prime mover 2. The cover 31 is fixed to theinput shaft 5 extending from the prime mover 2. For example, the cover31 includes a spline hole to which the input shaft 5 is spline-coupled.Because of this, the cover 31 is unitarily rotated with the input shaft5. The cover 31 is disposed to cover the turbine 33.

The cover 31 includes a disc portion 311, a cylindrical portion 312 anda cover hub 313. The disc portion 311 includes an opening in the middlethereof. The cylindrical portion 312 extends from the outer peripheralend of the disc portion 311 toward the prime mover 2. The disc portion311 and the cylindrical portion 312 are provided as a single member.

The cover hub 313 is fixed to the inner peripheral end of the discportion 311. In the present preferred embodiment, the cover hub 313 isprovided as a member separated from the disc portion 311. However, thecover hub 313 can be provided together with the disc portion 311 as asingle member.

The cover hub 313 includes a first boss portion 313 a, a first flangeportion 313 b and a protruding portion 313 c. The first boss portion 313a, the first flange portion 313 b and the protruding portion 313 c areprovided as a single member.

The first boss portion 313 a is made in the shape of a cylinderincluding a spline hole. The input shaft 5 is spline-coupled to thefirst boss portion 313 a. As shown in FIG. 2, the first boss portion 313a is rotatably supported by the torque converter casing 7 through abearing member 102. Because of this, the first boss portion 313 aaxially extends from the first flange portion 313 b to the opposite sideof the prime mover 2.

As shown in FIG. 3, the first flange portion 313 b extends radiallyoutward from the first boss portion 313 a. Detailedly, the first flangeportion 313 b extends radially outward from the prime mover 2-side endof the first boss portion 313 a. The disc portion 311 is fixed to theouter peripheral end of the first flange portion 313 b.

The protruding portion 313 c axially extends from the first flangeportion 313 b. The protruding portion 313 c extends toward the primemover 2. The protruding portion 313 c extends from the outer peripheralend of the first flange portion 313 b. The protruding portion 313 c hasa cylindrical shape. The protruding portion 313 c includes a pluralityof through holes 313 d. The hydraulic fluid is discharged from thetorque converter 3 through the through holes 313 d.

The impeller 32 is rotated unitarily with the cover 31. The impeller 32is fixed to the cover 31. The impeller 32 includes an impeller shell321, a plurality of impeller blades 322, an impeller hub 323 and aplurality of supply flow pathways 324.

The impeller shell 321 is fixed to the cover 31. The plural impellerblades 322 are attached to the inner surface of the impeller shell 321.

The impeller hub 323 is attached to the inner peripheral end of theimpeller shell 321. It should be noted that in the present preferredembodiment, the impeller hub 323 is provided together with the impellershell 321 as a single member but can be provided as a member separatedfrom the impeller shell 321.

The impeller hub 323 includes a second boss portion 323 a and a secondflange portion 323 b. The second boss portion 323 a has a cylindricalshape and axially extends. The second boss portion 323 a is rotatablysupported by the torque converter casing 7 through a bearing member 103(see FIG. 2). A stationary shaft 104 axially extends in the interior ofthe second boss portion 323 a. It should be noted that the stationaryshaft 104 has a cylindrical shape and the output shaft 6 axially extendsin the interior of the stationary shaft 104. Besides, the stationaryshaft 104 extends from, for instance, a reducer casing 42 or the torqueconverter casing 7. The stationary shaft 104 is non-rotatable.

The supply flow pathways 324 are provided in the impeller hub 323.Detailedly, the supply flow pathways 324 are provided in the secondflange portion 323 b. The supply flow pathways 324 extend radiallyoutward from the inner peripheral surface of the impeller hub 323.Additionally, the supply flow pathways 324 are opened to the interior ofa torus T. It should be noted that the torus T is a space enclosed bythe impeller 32 and the turbine 33.

The supply flow pathways 324 are axially closed. In other words, thesupply flow pathways 324 are through holes radially extending in theimpeller hub 323. As shown in FIG. 4, the supply flow pathways 324extend in a radial shape. The supply flow pathways 324 slant opposite toa forward rotational direction, while extending radially outward. Inother words, the supply flow pathways 324 slant in a reverse rotationaldirection (counterclockwise in FIG. 4), while extending radiallyoutward. It should be noted that the extending shape of each supply flowpathway 324 is not limited to a straight shape. For example, as shown inFIG. 5, each supply flow pathway 324 can extend in a curved shape.

As shown in FIG. 3, the turbine 33 is disposed in opposition to theimpeller 32. Detailedly, the turbine 33 is axially opposed to theimpeller 32. The turbine 33 is a component to which a torque istransmitted from the impeller 32 through the hydraulic fluid.

The turbine 33 includes a turbine shell 331, a plurality of turbineblades 332 and a turbine hub 333. The turbine blades 332 are fixed tothe inner surface of the turbine shell 331.

The turbine hub 333 is fixed to the inner peripheral end of the turbineshell 331. For example, the turbine hub 333 is fixed to the turbineshell 331 by at least one rivet. In the present preferred embodiment,the turbine hub 333 is provided as a member separated from the turbineshell 331. However, the turbine hub 333 can be provided together withthe turbine shell 331 as a single member.

The output shaft 6 is attached to the turbine hub 333. Detailedly, theoutput shaft 6 is spline-coupled to the turbine hub 333. The turbine hub333 is unitarily rotated with the output shaft 6.

The turbine hub 333 includes a third boss portion 333 a and a thirdflange portion 333 b. The third boss portion 333 a and the third flangeportion 333 b are provided as a single member.

The third boss portion 333 a has a cylindrical shape and includes aspline hole. The output shaft 6 is spline-coupled to the third bossportion 333 a. The third boss portion 333 a axially extends from thethird flange portion 333 b to the opposite side of the prime mover 2. Inother words, the third boss portion 333 a axially extends from the thirdflange portion 333 b toward the cover hub 313.

The third boss portion 333 a is disposed at a radial interval from theprotruding portion 313 c. In other words, the protruding portion 313 cis disposed radially outside the third boss portion 333 a. The firstone-way clutch 35 is disposed between the third boss portion 333 a andthe protruding portion 313 c. It should be noted that withoutinstallation of the first one-way clutch 35, the outer peripheralsurface of the third boss portion 333 a and the inner peripheral surfaceof the protruding portion 313 c are opposed to each other.

A flow pathway is provided between the cover hub 313 and the distal endof the third boss portion 333 a such that the hydraulic fluid flowstherethrough. In the present preferred embodiment, the third bossportion 333 a is provided with a plurality of cutouts 333 c on thedistal end thereof. The cutouts 333 c radially extend on the distal endof the third boss portion 333 a. The hydraulic fluid is discharged fromthe torque converter 3 through the cutouts 333 c and the through holes313 d.

The third flange portion 333 b extends radially outward from the thirdboss portion 333 a. Detailedly, the third flange portion 333 b extendsradially outward from the prime mover 2-side end of the third bossportion 333 a. The turbine shell 331 is fixed to the outer peripheralend of the third flange portion 333 b by the at least one rivet or soforth.

The stator 34 is configured to regulate the flow of the hydraulic fluid(hydraulic oil) returning from the turbine 33 to the impeller 32. Thestator 34 is rotatable about the rotational axis O. For example, thestator 34 is supported by the stationary shaft 104 through the secondone-way clutch 36. The stator 34 is disposed axially between theimpeller 32 and the turbine 33.

The stator 34 includes a stator carrier 341 having a disc shape and aplurality of stator blades 342 attached to the outer peripheral surfaceof the stator carrier 341.

The first one-way clutch 35 is disposed between the cover 31 and theturbine 33. The first one-way clutch 35 makes the cover 31 rotatablerelative to the turbine 33 in the forward rotational direction. In otherwords, when the prime mover 2 is forwardly rotated to move the vehicleforward, the first one-way clutch 35 is configured such that the cover31 is rotated relative to the turbine 33. Because of this, in forwardmovement of the vehicle, the first one-way clutch 35 does not transmit atorque from the cover 31 to the turbine 33.

By contrast, the first one-way clutch 35 makes the cover 31 rotateunitarily with the turbine 33 in the reverse rotational direction. Inother words, when the prime mover 2 is reversely rotated to move thevehicle backward, the first one-way clutch 35 is configured such thatthe cover 31 is rotated unitarily with the turbine 33. Because of this,in backward movement of the vehicle, the first one-way clutch 35transmits a torque from the cover 31 to the turbine 33.

The second one-way clutch 36 is disposed between the stationary shaft104 and the stator 34. The second one-way clutch 36 is configured tomake the stator 34 rotatable in the forward rotational direction. Bycontrast, the second one-way clutch 36 makes the stator 34 non-rotatablein the reverse rotational direction. The torque is transmitted from theimpeller 32 to the turbine 33, while being amplified by the stator 34.

The centrifugal clutch 37 is attached to the turbine 33. The centrifugalclutch 37 is unitarily rotated with the turbine 33. The centrifugalclutch 37 is configured to couple the cover 31 and the turbine 33 toeach other by a centrifugal force generated in rotation of the turbine33. Detailedly, the centrifugal clutch 37 is configured to transmit thetorque from the cover 31 to the turbine 33 when the rotational speed ofthe turbine 33 becomes greater than or equal to a predetermined value.

The centrifugal clutch 37 includes a plurality of centrifugal elements371 and a plurality of friction materials 372. The friction materials372 are attached to the outer peripheral surfaces of the centrifugalelements 371, respectively. The centrifugal elements 371 are disposedwhile being radially movable. It should be noted that the centrifugalelements 371 are disposed while being circumferentially immovable.Because of this, the centrifugal elements 371 are rotated together withthe turbine 33 and are moved radially outward by centrifugal forces.

When the rotational speed of the turbine 33 becomes greater than orequal to the predetermined value, the centrifugal clutch 37 isconfigured such that the centrifugal elements 371 are moved radiallyoutward and the friction materials 372 are engaged by friction with theinner peripheral surface of the cylindrical portion 312 of the cover 31.As a result, the centrifugal clutch 37 is turned to an on state, and thetorque outputted from the cover 31 is transmitted to the turbine 33through the centrifugal clutch 37. It should be noted that even when thecentrifugal clutch 37 is turned to the on state, the hydraulic fluid iscapable of flowing through the centrifugal clutch 37.

When the rotational speed of the turbine 33 becomes less than thepredetermined value, the centrifugal elements 371 are moved radiallyinward, whereby the friction materials 372 and the inner peripheralsurface of the cylindrical portion 312 of the cover 31, engaged byfriction, are disengaged from each other. As a result, the centrifugalclutch 37 is turned to an off state, and the torque outputted from thecover 31 is not transmitted to the turbine 33 through the centrifugalclutch 37. In other words, the torque outputted from the cover 31 istransmitted to the impeller 32 and is then transmitted to the turbine 33through the hydraulic fluid.

<Reducer 4>

As shown in FIG. 2, the reducer 4 is disposed axially between the primemover 2 and the torque converter 3. The reducer 4 transmits a torque,outputted from the torque converter 3, to the drive wheel 101 side.Detailedly, the reducer 4 amplifies the torque outputted from the torqueconverter 3 and transmits the amplified torque to the drive wheel 101side through a differential gear 109. It should be noted that thereducer 4 includes a plurality of gears 41 and the reducer casing 42accommodating the respective gears 41. It should be also noted that oneof the plural gears 41 is fixed to the output shaft 6. In the presentpreferred embodiment, one of the gears 41 is provided together with theoutput shaft 6 as a single member.

<Input Shaft 5>

The input shaft 5 extends from the prime mover 2. The input shaft 5extends toward the torque converter 3. The rotational axis of the inputshaft 5 is substantially matched with that of the prime mover 2 and thatof the torque converter 3.

The input shaft 5 inputs the torque, outputted from the prime mover 2,to the torque converter 3. The input shaft 5 is attached at the distalend thereof to the cover hub 313 of the torque converter 3. The inputshaft 5 is unitarily rotated with the rotor 23 of the prime mover 2. Theinput shaft 5 extends through the interior of the output shaft 6. Theinput shaft 5 is solid. The input shaft 5 includes a communicatingpathway 51 in the distal end thereof. The communicating pathway 51extends in the axial direction. Besides, the communicating pathway 51 isopened toward the first cooling flow pathway 9 a.

<Output Shaft 6>

The output shaft 6 outputs the torque outputted from the torqueconverter 3. The output shaft 6 outputs the torque, outputted from thetorque converter 3, to the reducer 4. The output shaft 6 extends fromthe torque converter 3 toward the prime mover 2.

The output shaft 6 has a cylindrical shape. The input shaft 5 extendsthrough the interior of the output shaft 6. The output shaft 6 isattached at one end (the right end in FIG. 2) to the turbine 33 of thetorque converter 3. On the other hand, the output shaft 6 is rotatablysupported at the other end (the left end in FIG. 2) by the reducercasing 42 through a bearing member 105.

<Torque Converter Casing 7>

As shown in FIG. 6, the torque converter casing 7 accommodates thetorque converter 3. In the present preferred embodiment, the torqueconverter casing 7 is provided together with the reducer casing 42 as asingle member. However, the torque converter casing 7 can be provided asa member separated from the reducer casing 42.

The torque converter casing 7 includes a side wall portion 71, an outerwall portion 72 and a plurality of heat dissipation fins 73. Thesidewall portion 71 is disposed in opposition to the cover 31 of thetorque converter 3. The sidewall portion 71 is disposed orthogonal tothe rotational axis O.

The torque converter 3 is disposed on one axial side (the left side inFIG. 6) of the sidewall portion 71. On the other hand, the sidewallportion 71 makes contact at the other side (the right lateral surface inFIG. 6) with external air. In other words, a member, functioning as aheat source, is not disposed on the other side of the sidewall portion71.

The cover 31 is rotatably attached to the middle part of the sidewallportion 71 through the bearing member 102. The sidewall portion 71 ismade of a material, having a high specific heat and a high thermalconductivity, so as to quickly absorb a large amount of heat from thehydraulic fluid flowing through the first cooling flow pathway 9 a andrelease the absorbed heat to the atmosphere. For example, the sidewallportion 71 is made of magnesium, aluminum or so forth.

The outer wall portion 72 is disposed in opposition to the outerperipheral surface of the torque converter 3. The outer wall portion 72is provided together with the sidewall portion 71 as a single member.However, the outer wall portion 72 can be provided as a member separatedfrom the sidewall portion 71. The outer wall portion 72 extends towardthe prime mover 2 from the outer peripheral end of the sidewall portion71. The outer wall portion 72 extends substantially in parallel to therotational axis O. It should be noted that the distal end (the primemover 2-side end) of the outer wall portion 72 slants radially inward.The outer wall portion 72 can be made of a similar material to thesidewall portion 71.

The heat dissipation fins 73 are provided on the sidewall portion 71.The heat dissipation fins 73 extend from the sidewall portion 71 to theopposite side (rightward in FIG. 6) of the torque converter 3. The heatdissipation fins 73 are attached to the sidewall portion 71 in order toefficiently dissipate the heat of the hydraulic fluid flowing throughthe first cooling flow pathway 9 a. The thermal conductivity of the heatdissipation fins 73 is preferably set to be equivalent to or higher thanthat of the sidewall portion 71 but is not particularly limited to thissetting. The heat dissipation fins 73 are made of, for instance,magnesium, aluminum, copper or so forth.

<First Cooling Flow Pathway 9 a>

The first cooling flow pathway 9 a is a flow pathway for cooling thehydraulic fluid discharged from the torque converter 3. The firstcooling flow pathway 9 a extends in the interior of the torque convertercasing 7. In the present preferred embodiment, the first cooling flowpathway 9 a is provided only in the upper half of the torque convertercasing 7 (see FIG. 2).

The first cooling flow pathway 9 a extends from the middle part to theouter peripheral part in the interior of the sidewall portion 71 andaxially extends therefrom beyond the torque converter 3 in the interiorof the outer wall portion 72. The first cooling flow pathway 9 a iscommunicated with the hydraulic fluid sump 8.

As shown in FIG. 7 or FIG. 8, the first cooling flow pathway 9 aincludes a plurality of paths in the interior of the sidewall portion71. In the present preferred embodiment, the first cooling flow pathway9 a is divided into two paths in the interior of the sidewall portion71. In the interior of the sidewall portion 71, the first cooling flowpathway 9 a extends from the middle part to the outer peripheral partnot in a straight shape but in a winding shape.

The first cooling flow pathway 9 a can include a plurality of paths inthe interior of the outer wall portion 72 as well. In the presentpreferred embodiment, the first cooling flow pathway 9 a is dividedinto, for instance, three paths in the interior of the outer wallportion 72. The first cooling flow pathway 9 a axially extends in astraight shape in the interior of the outer wall portion 72.Alternatively, the first cooling flow pathway 9 a can extend in awinding shape in the interior of the outer wall portion 72.

[Hydraulic Fluid Sump 8]

As shown in FIG. 6, the hydraulic fluid sump 8 is disposed to axiallyinterpose the torque converter 3 together with the sidewall portion 71therebetween. In other words, the hydraulic fluid sump 8, the torqueconverter 3 and the sidewall portion 71 are axially aligned in thisorder. The hydraulic fluid sump 8 is disposed in the interior of thereducer casing 42. The hydraulic fluid sump 8 is disposed above therotational axis O.

The hydraulic fluid sump 8 contains the hydraulic fluid to be suppliedto the torque converter 3 in the interior thereof. The hydraulic fluidsump 8 is provided with a supply port 81 in the bottom surface thereof.The hydraulic fluid, discharged from the supply port 81, is supplied tothe torque converter 3 through a flow pathway 106 provided between thestationary shaft 104 and the second boss portion 323 a of the impellerhub 323.

Specifically, a centrifugal force is generated in rotation of theimpeller 32 of the torque converter 3, whereby the hydraulic fluidresiding in the interior of the flow pathway 106 is supplied to theinterior of the torus T through the supply flow pathways 324. Then, thehydraulic fluid, discharged from the torque converter 3, flows to thefirst cooling flow pathway 9 a through the communicating pathway 51.Subsequently, the hydraulic fluid, cooled while flowing through thefirst cooling flow pathway 9 a, is returned to the hydraulic fluid sump8.

[Modifications]

One preferred embodiment of the present invention has been explainedabove. However, the present invention is not limited to the above, and avariety of changes can be made without departing from the gist of thepresent invention.

Modification 1

For example, as shown in FIG. 9, the torque converter unit can furtherinclude a second cooling flow pathway 9 b. The second cooling flowpathway 9 b extends through the interior of a compartment 107 of avehicle into which the torque converter unit is installed. The hydraulicfluid, discharged from the torque converter 3, flows through the secondcooling flow pathway 9 b. The hydraulic fluid, flowing through thesecond cooling flow pathway 9 b, is cooled while dissipating heatthereof into the compartment 107.

The hydraulic fluid is supplied to the second cooling flow pathway 9 bfrom the communicating pathway 51. Additionally, the hydraulic fluid isreturned to the hydraulic fluid sump 8 through the second cooling flowpathway 9 b.

The torque converter unit further includes a selector mechanism 11. Theselector mechanism 11 is configured to select either the first coolingflow pathway 9 a or the second cooling flow pathway 9 b as a coolingflow pathway for supplying the hydraulic fluid discharged from thetorque converter 3.

Modification 2

As shown in FIG. 10, the torque converter 3 can further include aplurality of elastic members 38. The elastic members 38 are disposedcircumferentially between the first one-way clutch 35 and the cover 31.The elastic members 38 transmit a torque, applied in the reverserotational direction from the cover 31, to the first one-way clutch 35.It should be noted that, when the cover 31 is rotated with respect tothe first one-way clutch 35 by more than a predetermined angle in thereverse rotational direction, first stopper surfaces 314 of the cover 31make contact with second stopper surfaces 351 of the first one-wayclutch 35. As a result, the torque, applied from the cover 31, isdirectly transmitted to the first one-way clutch 35.

In reverse rotation as described above, the torque, applied from thecover 31, is firstly transmitted to the first one-way clutch 35 throughthe elastic members 38, whereby massive and sudden torque transmissioncan be eased.

It should be noted that the elastic members 38 can be disposedcircumferentially between the first one-way clutch 35 and the turbine33. In this case, the elastic members 38 transmit a torque, applied fromthe first one-way clutch 35 in the reverse rotational direction, to theturbine 33.

Modification 3

As shown in FIG. 11, the present power transmission mechanism caninclude a planetary gear mechanism 400 and a clutch 401. The planetarygear mechanism 400 includes a sun gear 402, a plurality of planet gears403, a planet carrier 404 and a ring gear 405.

The sun gear 402 is attached to the input shaft 5. The sun gear 402 isunitarily rotated with the input shaft 5. The planet carrier 404 isattached to the output shaft 6. The planet carrier 404 is unitarilyrotated with the output shaft 6.

The clutch 401 is disposed between a non-rotatable member (e.g., thereducer casing 42 or the prime mover casing 21) and the ring gear 405.Besides, the clutch 401 is configured to brake rotation of the ring gear405.

The clutch 401 is, for instance, a one-way clutch. The clutch 401 makesthe ring gear 405 rotatable in forward rotation of the input shaft 5 andthe output shaft 6. By contrast, the clutch 401 makes the ring gear 405non-rotatable in reverse rotation of the input shaft 5 and the outputshaft 6.

According to this configuration, when the input shaft 5 and the outputshaft 6 are forwardly rotated, in other words, when the vehicle isforwardly moved, the ring gear 405 is being rotated without being fixed,whereby an amplifying action does not work in the planetary gearmechanism 400. Because of this, the torque, outputted from the primemover 2, is transmitted to the drive wheels 101 through the torqueconverter 3 and the reducer 4.

By contrast, when the input shaft 5 and the output shaft 6 are reverselyrotated, in other words, when the vehicle is backwardly moved, theclutch 401 makes the ring gear 405 non-rotatable, whereby the amplifyingfunction works in the planetary gear mechanism 400. Because of this, thetorque, outputted from the prime mover 2, is transmitted to the drivewheels 101 through the reducer 4, while being amplified by the planetarygear mechanism 400.

REFERENCE SIGNS LIST

-   2 Prime mover-   3 Torque converter-   31 Cover-   32 Impeller-   33 Turbine-   4 Reducer-   400 Planetary gear mechanism-   401 Clutch-   402 Sun gear-   403 Planet gear-   404 Planet carrier-   5 Input shaft-   6 Output shaft-   100 Drive unit

What is claimed is:
 1. A drive unit comprising: a prime mover; a torqueconverter to which a torque is inputted from the prime mover; and apower transmission mechanism disposed between the prime mover and thetorque converter, the power transmission mechanism configured totransmit the torque outputted from the torque converter toward a drivewheel.
 2. The drive unit according to claim 1, wherein the powertransmission mechanism is a reducer.
 3. The drive unit according toclaim 1, further comprising: an output shaft configured to output thetorque outputted from the torque converter; and an input shaft thatextends from the prime mover, the input shaft configured to input thetorque from the prime mover therethrough to the torque converter.
 4. Thedrive unit according to claim 3, wherein the output shaft extends fromthe torque converter toward the prime mover.
 5. The drive unit accordingto claim 3, wherein the output shaft has a cylindrical shape, and theinput shaft extends in an interior of the output shaft.
 6. The driveunit according to claim 3, wherein the torque converter includes a coverto which the input shaft is fixed, an impeller unitarily rotated withthe cover, and a turbine opposed to the impeller.
 7. The drive unitaccording to claim 6, wherein the impeller is disposed closer to theprime mover than the cover.
 8. The drive unit according to claim 3,wherein the power transmission mechanism includes a planetary gearmechanism including a sun gear, a planet gear, a planet carrier and aring gear, and a clutch configured to brake rotation of the ring gear,the sun gear is unitarily rotated with the input shaft, and the planetcarrier is unitarily rotated with the output shaft.
 9. The drive unitaccording to claim 8, wherein the clutch is a one-way clutch, the clutchconfigured to make the ring gear rotatable in forward rotation of theinput shaft and the output shaft, the clutch further configured to makethe ring gear non-rotatable in reverse rotation of the input shaft andthe output shaft.